1. Field of the Invention
This invention relates to a novel process for preparing a brassylic diester of the formula (I): EQU ROOC--CH.sub.2).sub.11 COOR (I)
wherein R is a lower alkyl group.
2. Description of the Prior Art
A brassylic diester can be hydrolyzed to brassylic acid and the two compounds are not only useful as a material for producing macrocyclic esters important as perfume musks but also they find much utility as materials for producing various polymers (e.g., polyamides, polyesters, etc.) and as plasticizers for polyvinyl chloride, polychloroethylene, etc.
Brassylic acid and esters are conventionally produced by oxidizing erucic acid in rapeseed oil with ozone or permanganic acid. However, it is becoming increasingly difficult to produce them from naturally occurring materials because the price of the rapeseed depends on the yield of its harvest, the acreage of rape fields in the world is decreasing, and Canada the world's largest rape producer is growing an increasing volume of a species with a small content of erucic acid.
Known processes for the synthesis of brassylic acid are (1) heating methyl undecylenate and ditertiary butyl peroxide in acetic acid for 48 hours, followed by hydrolyzing the reaction product (U.S. Pat. No. 3,308,140); (2) heating 2-ethoxycarbonylcyclododecanone with caustic alkali in diethylene glycol, followed by rendering the product acidic (Japanese Patent Publication No. 34406/71); and (3) reacting ethyl cyanoacetate with Br-(CH.sub.2).sub.10 COOC.sub.2 H.sub.5 in dimethylformamide, hydrolyzing the reaction product, followed by decarboxylation of the hydrolyzate [Dudinov A. A. et al., Izv. Akad. Nauk SSSR, Ser. Khim., 1974 (6), 1421-1423 (Chem. Abstracts, 81, 91013t, 1974)]. However, these processes are not necessarily acceptable as an industrial process primarily because the starting materials are not readily available.
Accordingly, various studies have been conducted directed to an industrial process for producing brassylic acid and it has now been found that brassylic diester can be easily prepared from 6,6'-methylenebis-(6-hexanolide) that is readily obtainable from available petrochemical products, and a method for preparing a high yield of 6,6'-methylenebis-(6-hexanolide) from 2,2'-methylenebiscyclohexanone has also been discovered.